In integrated circuit devices that are used in watches, real-time clocks and the like, there are cases where their oscillation circuits and logic circuits may use, for controlling power consumption, regulated voltages that are obtained through stepping down an external power supply supplied from outside of the integrated circuit device by using a regulator. In order to suppress the power consumption as much as possible, the closer the regulated voltage supplied from the regulator to a stop voltage of the integrated circuit device, the better. Here, the stop voltage means a voltage reached as the adjusted voltage is lowered with which the integrated circuit device does not operate. When the regulated voltage reaches the stop voltage, the system clock from the oscillation circuit is not outputted as a rectangular wave sufficient to operate a logic circuit in the succeeding stage, by which the function of the integrated circuit device stops.
For example, in an integrated circuit device for a real time clock, a voltage reduction by 10 mV is effective in reducing the power consumption of about 1 nW. Since the overall power consumption of such an integrated circuit device is about 30 nW, the reduction of 1 nW has a great significance. In this respect, methods for stably maintaining the regulated voltage to a low voltage have been proposed.
For example, as a constant voltage circuit to be used for a regulator, a circuit described in Japanese Laid-open Patent Application HEI 8-44449 is known. A low voltage circuit in accordance with the invention of Japanese Laid-open Patent Application HEI 8-44449 outputs an appropriate regulated voltage by suitably selecting the ratio between a resistor R1 and a resistor R2.
However, the stop voltage has temperature dependency, and the stop voltage generally becomes lower with higher temperatures in a CMOS circuit design. This is caused by the threshold voltage VT of the CMOS transistor that lowers with higher temperatures. From the viewpoint of lowering power consumption, it is preferred that the regulated voltage outputted from the regulator has the same temperature gradient as that of the stop voltage so as to maintain a constant potential difference with respect to the stop voltage at any temperatures. Therefore, among integrated circuit devices that require low power consumption, there are those that are capable of adjusting the regulated voltage to match with the operation temperature of the stop voltage in an output stage or the like of the constant voltage circuit.
A circuit described in FIG. 18 is an example of an internal circuit of a regulator for making adjustments according to changes in the temperature. A potential difference corresponding to a threshold voltage VTP of a P-type transistor is gained by a diode-connected transistor 900, and a potential difference corresponding to a threshold voltage VTN of an N-type transistor is gained by a transistor 901, such that VOUT correlated with VTP+VTN is outputted. By changing the regulated voltage based on the output VOUT, the regulated voltage can be lowered when the temperature rises.
However, the circuit shown in FIG. 18 makes the adjustment in an output stage of the regulator irrespective of the state of the rectangular wave that is outputted from the oscillation circuit. In other words, without judging the state of the actual rectangular wave outputted from the oscillation circuit, the regulated voltage is changed by the circuit shown in FIG. 18 having a structure different from that of the circuit for generating the rectangular wave. For this reason, in effect, a difference is generated in the temperature gradient with respect to that of the stop voltage.
In this case, as shown in FIG. 19, a temperature gradient 1020 of the stop voltage is different in inclination from a temperature gradient 1010 of the regulated voltage provided from the regulator circuit. Accordingly, only a regulated voltage with a sufficient margin from the stop voltage (for example, 70° C.) can be set so that the regulated voltage would not reach the stop voltage across the entire range of rated operation temperatures. In the example of FIG. 19, even in the case of operation in an environment normally at about 40° C., a large margin 1040 needs to be set, considering that it becomes close to the stop voltage at high temperatures (for example, at 70° C.).
Furthermore, the temperature gradient 1020 of the stop voltage and the temperature gradient 1010 of the regulated voltage indicated by solid lines show the characteristic in one condition (for example, a TYP condition) as in the process. In consideration of variations in the process at the time of manufacturing in addition to the above, for example, in FIG. 19, the temperature gradient 1020 of the stop voltage changes in the range between an upper limit 1020A and a lower limit 1020B. Similarly, the temperature gradient 1010 of the regulated voltage may be in the range between an upper limit 1010A and a lower limit 1010B. Therefore, in order for mass-produced products to continue operating at rated operation temperatures, the regulated voltage must be adjusted in consideration of the potential difference between the lower limit of the regulated voltage and the upper limit of the stop voltage (for example, a potential difference 1030).
In other words, when the temperature gradient 1020 of the stop voltage and the temperature gradient 1010 of the regulated voltage are different from each other in their inclination, the margin needs to be decided based on an assumption of a temperature condition in which the potential difference between the temperature gradient 1020 of the stop voltage and the temperature gradient 1010 of the regulated voltage is the narrowest, and further in consideration of variations in the process. For this reason, a large potential difference from the stop voltage would be generated, which makes it difficult to achieve lower power consumption.
The present invention has been made in view of the above-described problems. In accordance with some embodiments of the invention, an integrated circuit device or the like that realizes low power consumption through approximating the temperature gradient of the regulated voltage to the temperature gradient of the stop voltage, to maintain an appropriate potential difference thereof with respect to the stop voltage even when the temperature condition changes.